Induction furnace



Aug. 23, 1960 D. L. LOMBARD 2,950,374

INDUCTION FURN CE Filed March 3, 1959 s Sheets-Sheet 1 T1 2 1i 1 H J L Daniel L.Lombord ZMQV W ATTORNEY Aug. 23, 1960 D. L. LOMBARD 2,950,374

INDUCTION FURNACE Filed March 3, 1959 Sheets-She 2 Aug. 23, 1960 D. 1.. LOMBARD 2,950,374

INDUCTION FURNACE Filed March 3, 1959 3 She e 3 Fig.6

United States Patent INDUCTION FURNACE Daniel L. Lombard, Youngstown, Ohio, assignor to Lombard Corporation, Youngstown, Ohio, a corporation of Ohio Filed Mar. '3, 1959, Ser. No. 796,870

8 Claims. (Cl. 219-10.67)

This invention relates to apparatus for inductively heating metallic workpieces and more particularly to induction heating apparatus for aluminum and other similar metal billets which are subsequently used in an extrusion process.

In the usual extrusion process a metal billet is fist heated in a furnace to render it soft and plastic and thereafter inserted into an extrusion press billet container having a die at its forward end. When an extrusion ram is forced under high pressure into the other end of the container, the previously softened billet is forced through the die to form a continuous extrusion.

It has been found most expeditious and satisfactory to heat the billet prior to extrusion in an electrical induction furnace. In such a furnace the billet is placed within an electrically energized coil whereby eddy currents are induced in the metal to dissipate energy sufficient to heat up the billet to the desired temperature in a very short time. In order to most effectively perform an induction heating operation, the billet is placed within a coil structure formed from a series of axially spaced coils, each of which is connected to one phase of a polyphase alternating current source to produce a traveling magnetic field. In this manner the eifective field produced by the coils moves progressively from one end of the coil structure to the other. This produces a motor action on the billet, similar to the movement of a solenoid armature, which tends to eject the billet from one end of the coil structure. Accordingly, it becomes necessary to provide means for holding the billet within the coil assembly during a heating operation to prevent it from being ejected from the coil.

In order to determine the temperature of the billet during a heating operation, there is usually provided a thermocouple device having a pair of spaced members of dissimilar metal which abut the surface of the billet.

As the thermocouple is heated, it generates an electrical I potential which is utilized to actuate a suitable indicator device and/or automatic control means to deenergize the induction coils at the proper time.

In most prior art induction furnaces, the means for holding the billet within the coil during a heating operation took the form of a retractable stop member at the exit end of the coil, while the thermocouple means was in the form of a pair of prongs of dissimilar metal which projected beyond the billet-engaging surface of the stop. With this arrangement, the prongs would necessarily project into the end of the billet when it abutted the stop member. Difficulty has been found with such prior art devices, however, in that the stop member may be brought into contact with the end of the billet with great force,

or the billet may slam against the stop member due to the aforesaid motor action with the result that the.

prongs of the thermocouple which project from the aforesaid billet-abutting surface may be damaged.

When a heated billet is first placed in the container of an extrusion press, it has a cross-sectional area somewhat smaller than the cross-sectional area of the container.

During the extrusion of a billet, however, the extrusion ram initially upsets the billet against the forward end of the billet container, meaning that the end of the billet becomes swaged or thickened so that it fills the entire cross-sectional area of the container and, in most cases, precludes the escape of any air entrapped at the forward end of the container. Since the entrapped air cannot ordinarily escape via the trailing end of the billet, it must find its way through the extrusion die and, in the case of soft metals, causes protrusions or bubbles in the finished extrusion. Consequently, it becomes highly desirable to provide some means for the escape of air at the forward end of the billet.

The present invention has as one of its objects the provision of novel thermocouple means of the general type described above for measuring the temperature of a billet within an induction coil. In accordance with the. invention hereafter described, there are provided a pair of rails of dissimilar metal extending along the inner periphery of the induction coil and parallel to its central axis. These rails form the two members of a thermocouple assembly, and since they come into contact with the surface of the billet, they may be used to measure its temperature during a heating operation. The rails themselves are slotted to prevent the flow of eddy currents therein and consequent heating. In addition, means are provided for laterally holding the billet on the thermocouple rails to prevent it from being ejected from the coil during a heating operation. Thus, since the thermocouple rails are positioned adjacent a side of the billet rather than at its end very little, if any, damage can be incurred on the rails due to movement of the billet in the coil under the high forces produced by the magnetic field.

Another object of the invention resides in the provision of novel means for cutting slots or grooves along the longitudinal length of the surface of a billet which is to be heated in a manner such that the aforesaid thermocouple rails extend into the grooves during a heating operation. In this manner especially good thermocouple contact is provided between the billet and the thermocouple grooves, and at the same time the grooves provide a passage in the billet for the escape of air at its forward end during an extrusion operation.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification and in which:

Figure 1 is a top view of a billet heater embodying the present invention;

Figure 2 is a partially broken away side view of the induction coil of the present invention, together with the means for cutting slots along the longitudinal length of the billet;

Figure 3 is a cross-sectional view taken along line III-III of Figure 2, showing the position of the thermocouple rails within the induction coil;

Figure 4 is a cross-sectional view taken along line IV--IV of Figure 2, showing the position of the cutting members for producing slots in the side of a billet;

Figure 5 is a detailed view of the thermocouple rails showing the manner in which they are mounted within the induction coil;

Figure 6 illustrates examples of various cross-sectional configurations of the thermocouple rails; and

Figure 7 illustrates the manner in which the thermocouple rails may be laterally slotted.

Referring to Figures 1 and 2, the numeral 10 indicates generally the frame structure of an induction heating furnace. Supported on the frame 10 is an induction coil assembly 12 which may be of generally conventional design, and which is preferably of a type adapted; for use with a polyphase power system to produce a traveling magnetic field. At the entrance end of the coil assembly 12 is a V-tray 14 which is arranged to hold a billet lo in axial alignment with the coil prior to its being pushed into the interior of the coil assembly 12.. As will be understood, conveyor means 17 are provided to place a succession of billets 16 on the V-tray 14 one by one preparatory to their being loaded into the coil assembly 12.

To feed billets into the interior of coil assembly 12, there is provided a pusher rod 18 carried on an arm 2'3 which slides on two spaced bars 22 and 24. Reciprocatory motion is imparted to the arm 2% by means of a fluid motor, generally indicated at 26, which is carried on the frame ltl. At the exit end of the coil assembly 12 are a series of conveyor rolls 28 which may be continuously or selectively rotated to carry a heated billet to a discharge station, not shown.

The coil assembly 12 may be of the type shown in US. Patent 2,676,234, issued April 20, 1954 to R. V.

Lackner et al. This type of coil assembly will produce a traveling magnetic field which produces a motor or solenoid action tending to eject the billet from an end of the coil. As shown in Figure 2, the coil assembly may be in a plurality of sections A, B and C each of which is aligned end to end with the other sections to form a complete coil assembly, the respective sections being insulated from each other by annular insulating members 27 and 29. These sections are connected by electrical leads, not shown, to the separate phases of a polyphase alternating current source to produce the aforesaid traveling magnetic field. As illustrated, each of the coil sections is in the form of a helical electrical conductor which is formed from corresponding lengths of copper tubing 39 and a copper bar 32 placed in continuous lateral relation thereto. The outer surface of the helical conductor is covered by insulating material 34, substantially as shown. Water or another similar coolant may be circulated through the lengths of copper tubing 3t to carry away the heat produced by the inductive field.

At each end of the coil structure 12 is an insulating end board 36 or 38 which is secured to the frame by any suitable fastening means such as bolts. Steel clampmg ring assemblies 40 and 42 are fastened to the end boards 36 and .38 and encircle the ends of the outer periphery of a split stainless steel liner tube 44 which is insulated from the coil sections by a layer of insulating material as. As shown in Figure 2, each clamping ring assembly 46 or 42 comprises an annular insulating member 41 sandwiched between a pair of split annular steel members 43 and 45. A bifurcated hold-down device generally indicated at 48, extends through liner 44 and layer 4t? between the coil sections A, B and C at 52 and 54 and is provided with clamping members 56 and 58 which abut a billet during a heating operation.

As shown in Figures 2, 3 and 5, there are provided two rails of dissimilar metal 60 and 152 which are afiixed to the inner periphery of the liner 44 and extend parallel to the central axis of the coil assembly 12. The rails 60 and 62 are insulated from the liner 44 by means of mounting blocks 64 and 66 of fiberglass or other similar insulating material. Thus, when the billet is fed into the interior of the coil assembly 12 by means of pusher rod 18 and fluid motor 26, its surface will come into contact with the thermocouple prongs 6t and 62. After the billet is so positioned within the assembly, the air (or hydraulic) cylinder 50 is actuated to lower clamping members 56 and 58 and thereby hold the billet on the rails. Electrical circuit means, generally indicated at 68 in Figure 3, are connected through leads 7% and 72 to the rails 62 and 6t), respectively, such that the potential generated in the rails may be used to actuate indicating 7 devices and/or control means for deenergizing the coil after the billet reaches the proper temperature.

Referring to Figures 6 and 7, the thermocouple rails 69 and 62 may be in various cross-sectional configurations, but in any event they must be slotted along their longitudinal length to prevent the How of eddy currents therein which would ordinarily heat the rails to temperatures which might give rise to erroneous temperature readings. The embodiment of Figure 7 shows that the coil may be slotted laterally as well as longitudinally to prevent the flow of eddy currents.

As shown in Figures 1, 2 and 4, there is provided at the entrance end of the coil assembly 12. a generally annular member 74 which has an inner periphery slightly larger than the outer periphery of the billet which is to be inserted into the induction coil 12. The annular member 74 is flared as at '76, whereby the central axis of a billet entering the member 74 will be automatically aligned with the axis of the forward portion of the member 74 in, passing therethrough. At the bottom of the inner periphery of member 74 are two pointed cutting members and 82 which are in direct alignment with the thermocouple rails 60 and 62 in the induction coil 12. Thus, when pusher arm 18 and fluid motor 26 move a billet 16 forward it will necessarily be forced through the annular member 74 while cutting members 80 and 82 cut slots along the longitudinal length of the billet. When the billet passes from member 74 into the coil assembly 12, the thermocouple rails 60 and 62 will extend into these slots to thereby provide especially good thermocouple contact between the billet and the thermocouple rails. These slots also provide a means for escape of air at the forward end of a billet during an extrusion operation in the manner described above.

It can thus be seen that the present invention provides a thermocouple means for an induction heating furnace which is not subject to damage by the inductive forces produced during the billet-heating operation. At the same time, the invention has an auxiliary advantage in providing a means for escape of air at the forward end of a billet during an extrusion operation. Although the invention has been shown in connection with a certain specific embodiment only, it will be readily apparent to those skilled in the art that various changes in the form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

1 claim as my invention:

1. An induction furnace comprising an open-ended induction coil within which a workpiece is heated, a pair of workpiece-supporting rails of dissimilar metal extending parallel to the central axis of said coil and along the inner periphery thereof, and electrical circuit means connected to said rails for measuring the temperature of a workpiece positioned thereon.

2. An induction furnace comprising an open-ended induction coil within which a workpiece is heated, a pair of rails of dissimilar metal extendng parallel to the central axis of said coil and along the inner periphery thereof, electrical circuit means connected to said rails for measuring the temperature of a workpiece positioned thereon, and means for holding a'billet against said rails during a heating operation.

3. An induction furnace comprising an open-ended induction coil within which a workpiece is heated, a liner member for the inner periphery of said coil comprising a thin-walled metal tube of interrupted circumferential continuity, a pair of workpiece-supporting rails of dissimilar metal extending parallel to the central axis of said coil and adjacent the inner periphery of said liner member, insulating means separating said rails from the liner member, and electrical circuit means connected to said rails for measuring the temperature of a workpiece positioned thereon.

4. An induction furnace comprising an open-ended induction coil within which a workpiece is heated, a liner member for the inner periphery of said coil comprising a thin-walled metal tube of interrupted circumferential continuity, a pair of workpiece-supporting rails of dissimilar metal extending parallel to the central axis of said coil and adjacent the inner periphery of said linear member, said rails being split along their longitudinal lengths to prevent the flow of eddy currents therein, insulating means separating said rails from the liner member, and electrical circuit means connected to said rails for measuring the temperature of a workpiece positioned thereon.

5. An induction furnace comprising an open-ended induction coil within which a cylindrical workpiece is heated, a pair of workpiece-supporting rails of dissimilar metal extending parallel to the central axis of said coil and along the inner periphery thereof, electrical circuit means connected to said rails for measuring the temperature of a workpiece positioned thereon, a generally annular member positioned at one end of said induction coil, said annular member having its axis in alignment with the axis of said induction coil and an inner periphery slightly larger than the periphery of a workpiece which is to be heated in the coil, a pair of cutting prongs in alignment with said rails and extending radially inwardly from said inner perphery of the annular member, and means for forcing cylindrical workpieces through said annular member and into said induction coil whereby the prongs will cut grooves in said workpiece and the workpiece-supporting rails will extend into said grooves when the workpiece is positioned within said coil.

6. An induction furnace comprising an open-ended induction coil within which a work piece is heated, a pair of workpiece-supporting rails of dissimilar metal extending parallel to the central axis of said coil and along the inner periphery thereof, electrical circuit means connected to said rails of measuring the temperature of a workpiece positioned thereon, a member positioned at one end of said induction coil, an aperture in said member having a periphery in substantial alignment with the inner periphery of said coil and a central axis in alignment with the central axis of said coil, cutter members extending inwardly from the periphery of said aperture toward its central axis, said cutter members being in substantial alignment with the workpiece-supporting rails in said coil, and means for forcing a workpiece through said aperture and into the coil whereby the cutting members will cut grooves in said workpiece and the workpiecesupporting rails will extend into said groves when the workpiece is positioned within said coil.

7. An induction furnace comprising an open-ended induction coil within which a workpiece is heated, a pair of workpiece-supporting rails of dissimilar metal extending parallel to the central axis of said coil and along the inner periphery thereof, electrical circuit means connected to said rails for measuring the temperature of a workpiece positioned thereon, and means for cutting grooves in a workpiece as it is inserted into said coil whereby the rails of dissimilar metal will extend into said grooves when the workpiece is positioned in said coil.

8. The combination claimed in claim 7 and including means for holding the workpiece on said rails during a heating operation.

References Cited in the file of this patent UNITED STATES PATENTS 1,784,427 Goerig Dec. 9, 1930 1,821,832 Goerig et al. Sept. 1, 1931 2,676,234 Lackner et al. Apr. 20, 1954 2,703,495 Benninghoflf Mar. 8, 1955 2,780,706 Brogan Feb. 5, 1957 2,858,405 Kimbrough et a1 Oct. 28, 1958 

